The Engineering and Initial Results of a Transformable Low-cost Ultra-high Resolution PET Camera

We have developed an ultra-high resolution transformable PET camera that can be transfigured into a whole-body mode (83-cm detector ring diameter, 13-cm axial FOV) or a brain/breast (54-cm diameter, 21-cm axial FOV) mode. The camera has 12 rectangular detector modules, and the detector gap between adjacent modules is very small and remains constant for every configuration. Each module has a large detection area (13 cm times 21 cm) and 3,168 BGO detector crystals of 2.7 times 2.7 times 18 mm with built-in front-end electronics. To improve spatial sampling, the gantry rotates 30 with a fine step size of 1deg for each position, and the high-speed electronics and detector modules also rotate along with the gantry. This system uses only 924 photomultiplier tubes (PMT) by applying a low-cost high-resolution PMT-quadrant-sharing detector design. To compensate for the slower scintillation timing of BGO detectors, the camera is equipped with the "HYPER", high yield pile-up event recovery front-end electronics. A fast LED cross-reference PMT tuning method is used to maintain the PMT gain balance. The system has been constructed and tested for preliminary imaging characteristics. The system sensitivity is 4.2% for whole-body and 9.2% for brain/breast mode measured with Na-22 at center of FOV. For brain/breast mode, the transaxial image resolutions at 0, 10 cm were found to be 2.7 and 4.0 mm, respectively, while for whole-body mode, the image resolutions are 3.3 and 3.9 mm. The axial resolution ranges from 2.8 to 3.5mm for middle 7 detector rings. High quality Hoffman brain phantom images were obtained in both modes.